Attempts have been made to provide sorters for use by individual carriers. However, since the theory of sorting utilized in such equipment required multiple passes it was necessary for the carrier to manually remove sorted material from bins (called "sweeping") and return the sorted letters back to the original sorting apparatus. This was not only cumbersome but also often resulted in breakdown of the sort and hence would require another first or second sort on the disassembly of the order of the sorted letters.